In order to improve the reliability of electronic components, a resin coating is applied to an electronic component and a circuit board on which the electronic component is mounted, so that the electronic component is not affected by moisture and dust in an environment and is protected from vibrations and impacts.
Such a resin for coating needs to have high resistance to heat, excellent insulation, high flexibility, high resistance to wear, and high adhesion. The resin for coating includes at least one of acrylic resin, urethane resin, poly-olefin resin, and silicon resin. The resin is evenly applied in a liquid state. In the case of a resin containing a solvent, the resin is cured on a joint structure after volatilization, achieving a desired coating resin.
In recent years, particularly, circuit boards mounted in electronic controls around the engine rooms of vehicles need to be resistant to high temperatures of about 150° C. For water resistance of circuit boards, resins such as epoxy resin, urethane resin, and silicon resin are used in view of heat resistance and a gas barrier. Particularly, urethane resin has received attention because of its cost effectiveness.
A conventional urethane resin contains polyester polyol or polybutadiene as a base resin to prevent migration in a hot and humid environment (for example, see patent literature 1).